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Expert's Corner — mineral

Wetting to Predict Blotching

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Wetting to Predict Blotching

You can usually get a pretty good idea whether or not the wood you are using will blotch when a stain or finish is applied by wetting the wood.You can use any liquid, but water will raise the grain causing you to have to sand more. Mineral spirits (paint thinner) works well except if you intend to apply a water-based finish. Some residue oiliness may remain and cause the finish to fish eye—that is, bunch up into ridges rather than level out.Denatured alcohol would be better for this situation because it will totally evaporate. But it evaporates quickly, so you...

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TIP: Dating furniture by the finish used

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TIP: Dating furniture by the finish used

Because different finishes have been used at different times, it’s often possible to date furniture simply by the finish on it. In the 18th century and earlier, makers used whatever finish they had available, usually wax or linseed oil. If the maker lived near a port city, alcohol- or turpentine-soluble resins may have been available. By the 1820s, transportation had improved and shellac flakes, along with other alcohol-soluble resins, became widely available. Alcohol evaporates rapidly so these finishes dry fast and don’t collect dust. As a result, shellac became the overwhelmingly dominant finish used on almost all furniture and woodwork...

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TIP: Rubbing Lubricant Comparison

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Many different lubricants are recommended for rubbing out finishes with an abrasive. Here’s how they differ. The more waxy or oily the lubricant the better it reduces scratching and sandpaper clogging but the slower it cuts. The more watery the lubricant the more aggressive the cutting but the more pronounced the scratches. So wax is the most lubricating of the common lubricants suggested. Oil would be next, followed by a mixture of oil and mineral spirits. On the more aggressive side, straight mineral spirits (paint thinner) still provides some lubrication while allowing the abrasive to cut effectively. Soapy water provides...

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TIP: Dealing with Bubbles in a Finish

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TIP: Dealing with Bubbles in a Finish

Bubbles in a finish are more likely from brushing than from spraying, though it’s possible to get bubbles in a sprayed finish if you have the air pressure turned up real high. Bubbles are caused by the turbulence created by the brush gliding over the surface much more than from shaking or stirring the finish. The problem is worse if your shop is hot or if the finish and wood are at different temperatures. Because some formulations bubble less than others, especially with varnishes and water-based finishes, you can also switch to another brand, which may reduce the problem. To...

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TIP: Two tricks to successful French polishing

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There are two very useful tricks to getting good results when French polishing. The first is to achieve a one-foot-or-less “comet’s tail” trailing the pad as you move it over the surface—as shown in the accompanying picture. This tail is made by the alcohol in the French-polishing solution evaporating through the oil (also in the solution). If the tail is too long, the pad is too wet, and you’ll probably damage the surface. When the tail gets really short, just a couple of inches, this is the signal that you need to add more shellac, alcohol and oil (I use...

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